I know you have a solution and all, but PM2 should already be running on your Pi as part of the installation process.

Did you save your PM2 state before reboot? If you’re willing to experiment, remove the PM2 commands from your crontab and reboot your mirror. Once it’s back up, start the mirror with pm2 start mm, wait for the interface to appear and then enter pm2 save.

Once PM2 has saved the state, reboot your mirror and MM2 should start after a few seconds.